This invention relates to composite golf shafts having a tubular metallic core and a graphite filter reinforcing layer superimposed thereon. More particularly, the present invention is concerned with golf shafts for the irons in a set of golf clubs.
A considerable amount of effort has been expended in the past to remedy the deficiencies of tubular metal golf shafts by coating the metal tube with a resin-impregnated glass fiber. The use of such resin-impregnated glass fiber coatings on tubular metal shafted golf clubs provides a dampening effect on the vibrations normally experienced during play with such clubs. Unfortunately, however, such coatings have introduced other changes in the playing characteristics of the club employing such resin-impregnated glass fiber coatings.
In copending application Ser. No. 711,284, filed Aug. 3, 1976, a vastly improved composite golf shaft is disclosed which has at least two superimposed strips of sheet material of a resin-impregnated unidirectional continuous graphite fiber-reinforcement spirally wound on top of a tapered metal tubular shaft and a layer of woven fiberglass interposed between alternating strips of the resin-impregnated graphite fiber reinforcement. The shaft additionally and significantly has a layer of structural adhesive interposed between the first layer of resin-impregnated unidirectional graphite fiber reinforcing material and the metal core. One of the significant advantages of the aforementioned graphite fiber reinforced tubular metal golf club shaft is its relatively low weight. A golf club with such a low shaft weight has a lower center of gravity, thereby enhancing the effectiveness of the hitting mass.
As is readily appreciated, golf clubs are generally referred to as "woods" or "irons", depending upon the physical characteristics of the golf club head and shaft. For example, "woods" have club heads generally substantially fabricated from wood, although they do have a metal face, i.e. a striking surface for hitting the golf ball. Also, "woods" have shafts that are longer than shafts of "irons". The "irons" have heads, of course, which are fabricated substantially entirely from a metal, such as steel. Golf club irons typically have shafts that have larger tip diameters than golf club woods. As will be appreciated, the stresses to which a golf club shaft is subjected is a function, in part, of the type of head employed, e.g., whether it is an iron head or a wood head, as well as its intended use in play. Indeed, it has been found that golf clubs having heads formed from metals and shafts having tubular metal cores with fiber-reinforced layer superimposed thereon frequently suffer failure, i.e. breakage, near the point where the shaft joins the club head.